To provide a connection structure of a high frequency circuit substrate capable of producing a uniform impedance matching circuit, being free from an effect from a substrate even the substrates of different permittivity is disposed at close range, and further obtaining electromagnetic connection without physical connection.

A dielectric resonators 6, 8 are disposed on a inside plane of a case located between the substrates on which a signal line is to be connected in neighboring positions. Below a dielectric cylinder 6b, a microstrip line 1 and a microstrip line 1' corresponding to the signal to be connected are disposed, and the input side of the signal and the output side thereof are electromagnetically coupled via a dielectric resonator 6 or 8.